The present invention relates to an information reproducing device which copies information magnetically recorded on an information recording medium, and an information reproducing method for reproducing information copied on the information reproducing device by utilizing the magneto-optical effect.
Recently, the recording density of magnetic recording and optical recording has been greatly increased and the recording and reproducing techniques have been developed; consequently, there have been ever-increasing demands for higher-density information recording. Here, various means for recording information on a recording medium using a magnetic film and for reproducing the information have been known. For example, in the case of a magnetic disk used as a recording medium, after information has been magnetically recorded, leakage flux from a recorded mark is detected by using a ring head or a thin-film head. Moreover, in the case of a magneto-optical disk used as a recording medium, after information has been magnetically recorded (in this case, particularly referred to as thermo-magnetic recording), a light beam which has been narrowed down to approximately its diffraction limit is emitted to the medium, and a change in the magneto-optical effect occurring in the magnetic film at this time is detected.
Moreover, another method has been proposed in which after information has been recorded on a recording medium using a magnetic film, an information reproducing device having a magnetic substance is brought close to the recording medium so as to copy the magnetization direction of the information, and a light beam which has been narrowed down to approximately its diffraction limit is emitted to the information reproducing device so that a change in the magneto-optical effect occurring in the magnetic substance is detected. In this method, the information recorded on the recording medium is copied on the information reproducing device, and then reproduced.
FIG. 1 is an explanatory drawing that shows a reproducing method using a conventional information reproducing device. This information reproducing device has been reported in xe2x80x9cSignal Read-out Characteristic of Floating Magnetic Head Using Magnetic Garnetxe2x80x9d, THE INSTITUTE OF ELECTRONICS, INFORMATION AND COMMUNICATION ENGINEERS, TECHNICAL REPORT OF IEICE, MR97-84, CPM97-176 (1998-03), p.1-p.7. In the Figure, the encircled portion shows an enlarged view. A reproducing head is placed on a face of a magnetic recording medium 14 having recording bits 15 in which information is magnetically recorded. The reproducing head is a floating magnetic head in which a slider section 10 is supported by a suspension 3. The slider section 10 is constituted as follows: A magnetic garnet film 16 is formed on a GGG (gadolinium, gallium, garnet) substrate 18 through crystal growth, thereon is formed a reflection film 17 made of titanium and a protective film 19 made of SiO2. The slider section 10 faces the magnetic recording medium 14 on the protective film 19 side.
In this reproducing head, upon reproducing, a leakage magnetic flux from the magnetic recording medium 14 is copied onto the magnetic garnet film 16 with the result that respective magnetization directions maintained by recording bits 15, 15 . . . are formed on the magnetic garnet film 16. A laser beam is emitted onto the magnetic garnet film 16 so that copied information is reproduced by detecting a change in the magneto-optical effect. Since the magnetic garnet exhibits a great magneto-optical effect, a greater reproducing signal can be obtained by reproducing information from the magnetic garnet film 16. However, the problem with this reproducing head is that in the case of recording wavelengths of not more than 2 xcexcm, the amplitude of the reproducing signal drops greatly, failing to reproducing information recorded with a high density.
Moreover, Japanese Patent Application Laid-Open No. 62-75955 (1987) has suggested a magneto-optical recording/reproducing head using a garnet film. This magneto-optical recording/reproducing head has recording and reproducing functions, is provided with a head having the garnet film that exhibits in-plane magnetization, and copies or induces information from a magnetic recording medium. Then, by magneto-optically reproducing the magnetization direction of the garnet film, it is possible to obtain a reproduced signal with a high level. The information reproducing device using such a garnet film has been proposed by various other references (Japanese Patent Application Laid-Open No. 47-1244(1972), Japanese Patent Application Laid-Open No. 56-37839(1981), Japanese Patent Application Laid-Open No. 61-214260(1986), Japanese Patent Application Laid-Open No. 61-214261(1986), Japanese Patent Application Laid-Open No. 6-325422(1994), etc.).
In the case when the information reproducing device which uses the garnet having a high magneto-optical effect is used for magneto-optical reproduction, a reproduced signal having a high level is obtained; however, as described earlier, this device fails to reproduce information recorded with a high density. Moreover, none of the above-mentioned patent applications specifically disclose the dimension and the magnetic characteristics of the garnet film, and the dimension of the head, etc., making it difficult to put this device into practical use.
The present invention has been devised to solve the above-mentioned problems, and one objective of the present invention is to provide an information reproducing device which can copy and reproduce information of an information recording medium that has been recorded with a high density by using a magnetic-substance chip having single-magnetic domain structure. Moreover, another objective of the present invention is to provide an information reproducing head, an information recording/reproducing head and an information reproducing method, which are allowed to reproduce information of an information recording medium that has been recorded with a high density by using such an information reproducing device.
An information reproducing device of the present invention faces to an information recording film so as to copy a magnetic flux to be reproduced, characterized by including a magnetic-substance chip having mono-magnetic domain structure.
The magnetic substance forms stripe magnetic domains, and has a specific magnetic domain width in a demagnetization state in accordance with composition of the magnetic substance. In the present invention, the dimension of the magnetic-substance chip in the magnetic-domain forming direction is set smaller than the above-mentioned specific magnetic domain width; therefore, the magnetic-substance chip has the mono-magnetic domain structure. Therefore, in the case when the width dimension of the magnetic-substance chip is greater than a recording mark formed on an information recording film, the magnetic flux of the recording mark formed on the information recording film is copied on the magnetic-substance chip in an enlarged manner during reproduction. Here, since the magnetic-substance chip forms only one magnetic domain over the entire area, it can detect, with high precision, a change in the magneto-optical effect at the time of an inversion in the magnetization direction. In this case, although the minimum recording mark formed on the information recording film has a smaller dimension than the magnetic-substance chip, an area which is determined by the temperature distribution of the information recording film and the inclination of the magnetic-substance chip to the information recording film during reproduction is copied onto the magnetic-substance chip.
The information reproducing device of the present invention is characterized in that the magnetic-substance chip is being formed into a predetermined dimension by etching a magnetic substance that has been grown on a substrate.
Therefore, since the crystal growth of the magnetic-substance is made from a parent material that serves as the substrate, the magnetic-substance chip has an accurate magnetic characteristic in composition. Moreover, a plurality of magnetic-substance chips may be simultaneously form on the parent material by etching, and then, the parent material may be cut into pieces; thus, it is possible to easily manufacture a number of information reproducing devices.
The information reproducing device of the present invention is characterized in that the magnetic-substance chip includes a receiving face for receiving a magnetic flux from the information recording film and an irradiation face for being irradiated with a light beam for reproducing the magnetic flux that has been copied. Moreover, the irradiation face has a larger area than the receiving face of the magnetic flux.
Therefore, the dimension of the receiving face of the magnetic flux is set closer to the dimension of the minimum recording mark formed on the information recording film, and since the dimension of the irradiation face for reproducing the copied magnetic flux is large, the magnetic flux is accurately copied so that it is possible to obtain a reproducing signal with high level.
The information reproducing device of the present invention is characterized in that a magnetization permeable film for allowing the magnetic flux to pass and to be copied onto the magnetic-substance chip is formed on the receiving face of the magnetic-substance chip.
In the present invention, the magnetization permeable film is a magnetic film having a high permeability. The magnetization permeable film is formed at a part of the magnetic-substance chip and faces at the information recording film. Therefore, the recording mark of the information recording medium that are closest to the opposing magnetization permeable film are copied. Consequently, even if the recording marks on the information recording film are fine, the magnetic flux is copied with high precision.
The information reproducing device of the present invention is characterized in that the magnetic-substance chip is made of a magnetic oxide having magnetic garnet structure that contains a rear earth metal, a transition metal and oxygen ions.
Therefore, since the magnetic oxide having the magnetic garnet structure exhibits a great magneto-optical effect, the copied magnetic flux is reproduced with a greater signal level.
The information reproducing device of the present invention is characterized in that the magnetic-substance chip has an irradiation face that is irradiated with a light beam for reproducing a copied magnetic flux, and further comprises a reflection film, on the side of apposing the irradiation face, for reflecting the light beam.
Therefore, the reflection film reflects the light beam with which the magnetic-substance chip is irradiated so that the light beam transmitting toward the information recording film can be reduced, thereby making it possible to increase the quantity of light received for obtaining a reproducing signal.
The information reproducing device in accordance with the present invention is characterized in that the magnetic-substance chip is a soft magnetic film having a perpendicular easy axis of magnetization.
Therefore, since the magnetic-substance chip has the perpendicular easy axis of magnetization, the irradiation direction of the light beam to the information reproducing device is determined in accordance with the magnetization direction of the magnetic-substance chip to the information recording film, the magnetic-substance chip facing to the information recording film. Consequently, it is possible to obtain an accurate reproducing characteristic.
The information reproducing head in accordance with the present invention is characterized by comprising the above-mentioned information reproducing device and a slider that has the information reproducing device attached thereto and is placed opposite to an information recording medium having the information recording film.
Since the slider is placed opposite to the medium, the magnetic-substance chip is facing closer to the information recording film so that information is copied and reproduced. With respect to the slider, the parent material for the magnetic-substance chip of the information reproducing device may be used as it is, or the parent material and the magnetic-substance chip may be attached to a slider section made of, for example, a synthetic resin.
The information reproducing head in accordance with the present invention is characterized by comprising the above-mentioned information reproducing device and an optical waveguide having a tip to which the information reproducing device is attached, with the tip being placed opposite to an information recording medium having the information recording film.
Since the tip of the optical waveguide, such as an optical fiber, is placed opposite to the medium, the magnetic-substance chip is facing closer to the information recording film so that information is copied and reproduced.
The information reproducing head in accordance with the present invention is characterized in that the magnetic-substance chip is arranged with its easy axis of magnetization being aligned substantially in parallel with the thickness direction of the information recording film.
Therefore, in the case when the information recording film is a perpendicular magnetization film or an in-plane magnetization film, a leakage magnetic flux from the information recording film is allowed to form a closed magnetic path, with the result that the perpendicular component of the magnetic flux is copied onto the magnetic-substance chip, and reproduced.
The information reproducing head in accordance with the present invention is characterized in that the magnetic-substance chip is arranged with the direction of its easy axis of magnetization being aligned crossing to the thickness direction of the information recording film.
Therefore, in the case when the information recording film is a perpendicular magnetization film or an in-plane magnetization film, a leakage magnetic flux from the information recording film is allowed to form a closed magnetic path, with the result that the in-plane component of the magnetic flux is copied onto the magnetic-substance chip, and reproduced.
The information recording/reproducing head in accordance with the present invention, which is a recording/reproducing head that has the above-mentioned information reproducing device and that records and reproduces information by relatively moving an information recording medium having the information recording film, is characterized by comprising the above-mentioned information reproducing device, a slider that is placed so as to face the information recording medium to which the information reproducing device is attached, and a magnetic head section for applying a magnetic field to the information recording medium, the magnetic head section being placed on the rear side in the shifting direction of the information reproducing device.
Upon recording information on the information recording film, the information is magnetically recorded by applying a magnetic field onto the information recording film by the magnetic head section. Alternatively, the information reproducing device is irradiated with a light beam so as to heat the information recording film and a magnetic field is applied to the information recording film by the magnetic head section, so that the information is magneto-optically recorded.
The information recording/reproducing head in accordance with the present invention, which is a recording/reproducing head that has the above-mentioned information reproducing device and that records and reproduces information by relatively moving an information recording medium having the information recording film, is characterized by comprising the above-mentioned information reproducing device, an optical waveguide having a tip to which the information reproducing device is attached, with the tip being placed opposite to the information recording medium, and a coil section that is wound around the tip of the optical waveguide.
Upon recording information on the information recording film, the information is magnetically recorded by applying a magnetic field to the information recording film from the coil section. Alternatively, by applying a light beam onto the information reproducing device attached to the tip of the optical waveguide such as an optical fiber so as to heat the information recording film, while a magnetic field is applied to the information recording film from the coil section, the information is magneto-optically recorded.
The information reproducing method in accordance with the present invention, which is an information reproducing method for reproducing information from an information recording medium having an information recording film, is characterized by comprising the steps of: placing a magnetic-substance chip having mono-magnetic domain structure so as to face the information recording film; copying a magnetic flux of a first area of the information recording film to the entire area of the magnetic-substance chip; moving the information recording medium with respect to the magnetic-substance chip, relatively; copying a magnetic flux in a second area adjacent to the first area of the information recording film to the entire area of the magnetic-substance chip; and irradiating the magnetic-substance chip with a light beam, so that a change in the magneto-optical effect of the magnetic-substance chip is detected during the information recording medium relatively moves.
Therefore, since the magnetic flux of the first area of the information recording film is copied onto the entire area of the magnetic-substance chip having mono-magnetic domain structure, a short recording mark that has been recorded on the information recording film with a high density is copied in an enlarged manner. Moreover, since the magnetic-substance chip forms only one magnetic domain with its entire area, the reproducing process is carried out by detecting a magnetization inversion within the entire area of the magnetic-substance chip so that a reproducing signal with a high level is obtained with an improved reproducing characteristic.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.